1. Field of the Invention
This invention relates to an instrument and system for pharmacologic measurement measuring a change in electric signal caused by a pharmacologic action or an electrophysiologic action of a biologic specimen, and a well vessel used therein.
2. Description of the Related Art
Conventionally, there has been known a technique for measuring the electrophysiologic action of a cell. Such a technique is used in, for example, screening medicines with the electrophysiologic action of the cell as an index. The electrophysiologic action of a cell mainly refers to an activity of an ion channel. In a cell, ion concentrations inside and outside the cell membrane change in company with a change in ionic permeability corresponding to the activity of an ion channel. Therefore, the measurement of a change in potential at a cell membrane enables measurements of activity of an ion channel (an electric action of a cell) such as the time required for gating of an ion channel, the timing thereof and the number of times of gating of the ion channel.
As a method for measuring a change in potential at a cell membrane, a method has been known in which an electrode for measuring an extracellular potential made of glass or an electrode made of a metal (such as platinum) is installed in the vicinity of a cell using a micromanipulator or the like to thereby measure the change. As another method, there has been a method in which a similar electrode is stuck into a cell to thereby measure a change in intracellular potential.
According to the above methods, an activity of an ion channel of a cell can be measured quantitatively and minutely. Skill in the technique is required in preparation or operation of an electrode and much time is required in measurement of one specimen, which makes the methods not suitable for high speed screening covering a great amount of compounds of medicine candidates. In addition, it is easy to damage a cell with these methods.
A quantitative measurement on an ion channel conducted in an electrode sticking method is not necessarily required in application of a high speed medicine screening, especially in first screening (selection of first candidates) and in the application, a qualitative detection of closing/opening of an ion channel satisfies requirement and quickness and convenience are given a more serious consideration; therefore, it is thought that an extracellular potential recording method using a flat plate electrode is suitable for such an application (JP No. 2949845, U.S. Pat. Nos. 5,810,725, 5,563,067, JP A No. 9-526737 and U.S. Pat. No. 5,187,069).
An extracellular potential recording method using a flat plate electrode is based on a principle that by placing a flat plate electrode on a biologic specimen in a solution having a composition close to an intravital salt concentration to measure a change in potential at an electrode, an ionic flow passing through an ion channel can be measured. That is, the method uses a phenomenon that an electrophysiologic action of a cell causes a change in potential at the electrode installed in the vicinity of the cell.
Because this extracellular potential recording method only involves placing a cell on a flat plate electrode without sticking an electrode into a cell, an electrophysiologic action of a cell can be measured conveniently and quickly. Since a semiconductor processing technique can be applied in preparation of a flat electrode, a great number of microelectrodes can be formed on a base substrate. Hence, the method is suitable for a high speed screening in various kinds of medicines.
A change in electric signal caused by an electrophysiologic action of a cell is, however, very weak and becomes weaker since such a change in signal is detected through a solution in an extracellular potential recording method using a flat plate electrode. Therefore, in order to ensure a high precision measurement, a necessity arises for detection of a change in electric signal caused by an electrophysiologic action of a cell with good sensitivity.
In order to detect a microsignal with a good S/N ratio, it is required that, generally, a measurement section should be electrostatically shielded so that an external disturbance noise is mixed into a measurement system (M. Krause, S. Ingebrandt, D. Richter et al., Extended gate electrode arrays for extracellular signal recordings, Sensor and Actuators B 70 (2000) pp. 101 to 107). In order to use the method in application to a high speed screening in medicines, all of a measurement section cannot be electrostatically shielded. High speed screening in various kinds of medicines requires exchange of plural kinds of medicinal solutions in a short time with a simple construction. Hence, construction of a sensor base substrate and an apparatus is more complex in mechanisms each injecting/discharging a solution are individually provided to respective solution holding sections and at the same time transferring of the solutions to be controlled. Exchange of medicinal solutions is realized in a following way. XY moving type solution injecting/discharging devices in a row are driven above the solution holding sections so as to add or suck the solutions each having a prescribed unit volume to or from the solution holding sections from above in a batch mode. In the batch mode solution adding/sucking method, however, a necessity arises for forming an opening section through which injection to a solution surface is conducted, which negates electrostatic shielding of the measuring section. As a result, an external disturbance accompanying dropping of a solution is generated at a value as large as not to be neglected relative to a microelectric signal. An external disturbance generated in company with exchange of solutions continues for a long time even after dropping of a solution is over. Hence, a problem arises that it is impossible to measure a response of an ion channel caused by a reaction on a small scale with a medicine and a response of gating of ion channel in rapid inactivation in which the ion channel is activated within a short time from exchange of medicines and thereafter, inactivated.